a(n) = nextprime(7^n)-7^n.

Terms

a(0) =1a(1) =4a(2) =4a(3) =4a(4) =10a(5) =4a(6) =10a(7) =4a(8) =16a(9) =4a(10) =18a(11) =10a(12) =16a(13) =40a(14) =4a(15) =66a(16) =6a(17) =24a(18) =48a(19) =24a(20) =16a(21) =52a(22) =102a(23) =4a(24) =46a(25) =60a(26) =10a(27) =24a(28) =76a(29) =10